Droplets Manipulation Based On Electrowetting-on-dielectric And Its Application In Immunoassay

Electrowetting-on-dielectric(EWOD),as a microfluidic phenomenon,has been widely used in digital microfluidic systems.Digital microfluidic technology based on EWOD is a new droplet manipulation technology.It can manipulate droplets from picoliters to microliters on planar electrode arrays,and perform operations including droplet generation,merging,mixing,and splitting.Therefore,the physical mechanism of EWOD-based droplet actuation is the theoretical basis for studying digital microfluidic liquid processing and realizing various biochemical applications.Immunosensing is a sensitive and powerful analytical tool.Optical,electrical and other immunosensing strategies show unique advantages when combined with digital microfluidic systems.For example,processing small-volume reagent droplets can effectively reduce molecular diffusion time,improve experimental efficiency and detection throughput,reduce reagent costs.In addition,the fully automatic droplet processing can effectively reduce the complexity of the sample processing and increase automation.In conclusion,the work is developed from exploring the physical mechanism of EWOD-based droplet manipulation,realized chemiluminescence and electrochemical immunosensing based on digital microfluidic technology,and performing specific immunodetection of specific protein molecules.1.In the paper,we first briefly introduce the EWOD effect,and summarize the development of EWOD-based digital microfluidic technology at home and abroad.Then,we review the digital microfluidic technology,immunosensing technology and biosensing based on digital microfluidic technology.The advantages and significance of digital microfluidics in immunosensing are analyzed and summarized.2.We studied on the droplet manipulation mechanism and droplet dynamics based on EWOD.The origin of Young’s equation starting from the surface tension of the droplet was discussed.Based on the classical thermodynamic model,we theoretically analyzed electrowetting and dielectric wetting,and explained the Young-Lippmann equation.Then,we discussed the EWOD force for droplet movement from thermodynamic and electrical aspects,and analyze the factors that affect the EWOD force.When the droplet is moved by the EWOD force,we investigate the contact angle hysteresis effect of the droplet and its formation.Finally,for EWOD droplet manipulation,we theoretically explore the droplet moving speed and droplet splitting.3.We performed research on the influence of electrode structure on EWOD-based droplet manipulation.The finite element simulation model based on the double-plate enclosed digital microfluidic chip was established with square and hexagonal electrode.The theoretical simulation of droplet manipulation in the chip is carried out via "Phase field" method and "Creeping flow" method.We fabricated digital microfluidic chips with the same electrode structure.We carried out the experiments of the effect of voltage on the volume of generated droplets.Based on theoretical simulations and experimental results,we discussed the effects of square and hexagonal electrode structures on droplet splitting speed,droplet formation and droplet movement.It is demonstrated that hexagonal electrodes prevail square electrodes in faster droplet splitting speed and more stable droplet generation.4.We proposed a droplet generation method for bidirectional droplet splitting on a digital microfluidic chip.This method splits a large droplet into three sub-droplets with high aspect ratios,without changing the chip geometry.By combining the advantages of this droplet generation method,we integrated a magnetic suction module,an optical detection module,a three-axis control module and a droplet drive system to establish a digital microfluidic-based magnetic particle chemiluminescence immunodetection platform.The platform is capable of highly efficienct immunomagnetic bead washing.We finally achieved parallel detection of five B-type natriuretic peptide samples.It demonstrates the platform’s ability to increase assay throughput and rapidly analyze physiological samples.5.By combining digital-microfluidic-based droplet manipulation with electrochemical impedance immunodetection,we carried out research on electrochemical immunosensing based on digital microfluidics.We first verified the feasibility of electrical impedance immunosensing by using laser-rapidly fabricated gold electrodes.We characterize the electrode performance by finite element analysis and PBS measurements,and biofunctionalize the gold electrode surface.We achieved electrical impedance immunodetection with mouse Ig G.We optimized the electrode design based on the results of the feasibility experiments.We fabricated interdigitated gold electrodes on the top plate of a digital microfluidic chip for immunosensing.Through finite element analysis and on-chip sample dilution,we verified the electrode sensing performance and droplet manipulation ability respectively.Finally,we realized electrical impedance immunodetection with low-concentration mouse Ig G on a digital microfluidic chip.